1. Field of the Invention
The present invention relates to a maleic anhydride copolymer. In particular, this invention relates to a novel copolymer comprising maleic anhydride, a conjugated diene(s) and an aliphatic monoolefin(s), a process for preparing the copolymer, hydrolyzed products of the copolymer, and applications of the hydrolyzed products to scale inhibitors, dispersants for calcium carbonate and admixtures for cement and concrete.
2. Description of the Related Art
Copolymers of maleic anhydride and olefins have been well known. U.S. Pat. No. 3,491,068 discloses copolymers maleic anhydride and a conjugated diene(s). U.S. Pat. Nos. 3,553,177, 3,560,455, 3,560,456 and 3,560,457 disclose copolymers of maleic anhydride and an .alpha.-olefin(s).
The maleic anhydride-conjugated diene copolymers are known to be used as dye-assist agents, adhesives, fire-extinguishing agents, casting mold release agents and restaining inhibitors for detergents. However, they have not been utilized as scale inhibitors, dispersants for inorganic pigment and admixtures for cement and concrete.
The maleic anhydride-.alpha.-olefin copolymers are known to be used as casting mold release agents, slip agents and floor polishes since the copolymer has good wax properties. Further, hydrolyzed products of the copolymer are known to be used as adhesives, scale inhibitors, dispersants for inorganic pigment and admixtures for cement and conctrete.
However, the hydrolyzed maleic anhydride copolymers do not show sufficient properties required for scale inhibitors, dispersants for inorganic pigment or admixtures for cement and concrete. What kind of properties are required in these applications is mentioned in detail below.
Scale inhibitors are added to cooling water of heat exchangers, water of boilers, evaporators and the like for prevention of scale formation.
Water such as natural water, tap water and industrial water contains various impurities. The impurities are cations such as calcium, magnesium, iron and barium, and anions such as carbonate ions, hydrogen carbonate ions, sulfuric acid ions and silicate ions. Occasionally, zinc ions and phosphoric acid ions are contained as corrosion inhibitors. The above water is utilized as circulating water of equipment such as heat exchangers, boilers and evaporators.
The water is often heated, cooled or concentrated, or the pit of the water is altered in the equipment. As a result, the ions contained in the water change to insoluble salts, and the salts deposit and adhere on inner walls of the equipment to form scales. The adhered scales reduce heat transfer efficiency and cooling efficiency, increase flow resistance, or cause corrosion of equipment.
In order to solve these problems, scale inhibitors are used. Previously known inhibitors are lignin compounds, phosphorus compounds, polyacrylic acid compounds and polymaleic acid compounds. Among them, the polymaleic acid compounds such as hydrolyzed products of maleic anhydride homopolymers and maleic anhydride-monoolefin copolymers are known to be relatively good scale inhibitors (see Japanese Patent Publication (KOKOKU) Nos. 53-20475 and 54-29998, and Japanese Patent (KOKAI) Nos. 53-70089 and 60-71093).
However, when the hydrolyzed product of the maleic anhydride copolymer is used in relatively low concentration, the inhibitory effect on adhesion of scales is still insufficient. Further, adhesion of scales comprising iron as a main component is not supressed by the hydrolyzed product adequately. Thus, improved scale inhibitors are required.
Among the known inhibitors, the hydrolyzed product the maleic anhydride homopolymer shows relatively good properties as mentioned above. However, the production of the homopolymer requires a large amount of polymerization initiator. The polymerization initiator is relatively expensive and, therefore, the homopolymer utilizing the initiator is also expensive.
Dispersants for inorganic pigment are important in the paper and paint industry. The dispersants are added to inorganic pigments such as calcium carbonate, titanium oxide or clay to produce a high concentration aqueous slurry in order to reduce the viscosity of the slurry (improvement in dispersibility) and suppress the rise of viscosity with time (improvement in stability of dispersibility).
A high concentration aqueous slurry containing as little water as possible and having low viscosity is preferred. This is because when white pigments such as calcium carbonate are applied on a paper, drying energy can be saved, and good coating workablity and performance are obtainable. Further, from the viewpoint of transfer and storage, an aqueous slurry with improved stability of dispersibility is necessitated since the aqueous slurry often precipitates during transer or storage to form a hard cake. Therefore, it is expected that a dispersant enables one to provide a high concentration aqueous slurry even if it is utilized in a small amount.
Condensed phosphorares such as pyrophosphorates and hexametaphosphorates, zinc salts and silicates are known as inorganic dipsersants. Salts of polycarboxylic acid such as polyacrylic acid and hydrolyzed products of maleic anhydride-isobutene coplymers are known as organic dipsersants (see Japanese Patent Disclosure (KOKAI) Nos. 60-99334 and 62-132730).
A large amount of inorganic dispersants is required to be added to an aqueous slurry because the stability of dispersibility is bad. As a result, the obtained slurry ms expensive and the coating performance is low. The organic dispersants have better properties than the inorganic ones. However, the organic ones cannot provide good dispersibility to precipitated calcium carbonate with 1.mu. or less of particle size and are required to be improved.
Dispersants called admixtures for cement and concrete are usally added to cement mixtures to increase flowability and to improve placing workability. Cement mixtures comprise cement, water, sand and gravel. The strong cohesive force of cement particles makes the placing workability poor. In order to improve the workability, it is required to increase the water content in the cement mixture and to make the flowability high. However, the increase of water content results in a reduction of cement content in the cement mixture. This leads to lowering of strength of the hardened cement mixture.
The flowability of kneaded cement mixtures is gradually decreased due to aggregation of cement particles with the elapse of time. The kneaded cement mixtures are placed at certain intervals after kneading. However, kneaded cement mixtures are transferred to a placing site (construction site) and the intervals from kneading to placing may be widely varied due to a transfer distance and traffic jams. Therefore, the flowability of cement mixtures at the placing site is altered each time and it is hard to obtain constant workability.
Reduction of flowability with time causes another problem in the production of concrete secondary products such as piles, poles or blocks. When the transfer of kneaded cement mixture under increased pressure is interrupted and resumed after a few minutes, if the flowability of the cement mixture is lowered during the interruption, the pressure in the transfer piping is rapidly increased or piping of the transfer system is blocked.
For solution of the above mentioned problems, the admixtures for cement and concrete are used and formalin condensates of sodium naphthalene sulfonate are known (see Japanese Patent Disclosure (KOKOKU) No. 41-11737).
However, the formalin condensates of sodium naphthalene sulfonate are not a sufficient admixture. This is because good flowability provided by the condensate is not retained for a long period of time but is retained temporarily.
An object of the present invention is to provide a scale inhibitor which enables to inhibit deposition and adhesion of scale containing calcium and iron as main components even if the concentration of the inhibitor is relatively low, at which the known maleic anhydride copolymers does not function sufficiently.
Another object of the present invention is to provide a scale inhibitor which can be produced with a small amount of polymerization initiator and, as a result, is not expensive.
A still another object of the present invention is to provide a dispersant for inorganic pigments, in particular a dispersant for calcium carbonate, which offers excellent stability of dispersibility and which provides low viscosity to a high concentration slurry even if the added amount is small.
Another object of the present invention is to provide an admixture for cement and concrete which enables one to improve dispersibility of cement mixtures by suppressing physical and chemical aggregation of cement particles contained in kneaded cement mixtures.
Still another object of the present invention is to provide an admixture for cement and concrete which enables one to provide good flowability to cement mixtures and to prevent a reduction of flowability with time (slump loss).